A worker shovels sand Monday onto a line of Hesco baskets put in place in anticipation of Tropical Sorm Isaac, which is expected to make landfall on the Louisiana coast as a hurricane, in Port Sulphur, La.. (ASSOCIATED PRESS / Gerald Herbert)

NEW ORLEANS (AP) — With its massive size and ponderous movement, Tropical Storm Isaac was gaining strength Monday as it headed toward the Gulf Coast. The next 24 hours would determine whether it brought the usual punishing rains and winds — or something even more destructive harkening back to the devastation wrought seven years ago by Hurricane Katrina.

The focus has been on New Orleans as Isaac takes dead aim at the city, but the impact will be felt well beyond the city limits. The storm's winds could be felt more than 200 miles from the storm's center.

The Gulf Coast region has been saturated thanks to a wet summer, and some officials have worried more rain could make it easy for trees and power lines to fall over in the wet ground. Too much water also could flood crops, and wind could topple plants such as corn and cotton.

"A large, slow-moving system is going to pose a lot of problems: winds, flooding, storm surge and even potentially down the road river flooding," said Richard Knabb, director of the National Hurricane Center in Miami. "That could happen for days after the event."

The storm's potential for destruction was not lost on Alabama farmer Bert Driskell, who raises peanuts, cotton, wheat, cattle and sod on several thousand acres near Grand Bay, in Mobile County.

"We don't need a lot of water this close to harvest," Driskell said.

However, Isaac could bring some relief to places farther inland where farmers have struggled with drought. It also may help replenish a Mississippi River that has at times been so low that barge traffic is halted so engineers can scrape the bottom to deepen it.

Forecasters predicted Isaac would intensify into a Category 2 hurricane, with winds of about 100 mph, by early Wednesday around the time it's expected to make landfall. The current forecast track has the storm aimed at New Orleans, but hurricane warnings extended across 280 miles from Morgan City, La., to the Florida-Alabama state line. It could become the first hurricane to hit the Gulf Coast since 2008.

Evacuations were ordered for some low-lying areas and across the region, people boarded up homes, stocked up on supplies and got ready for the storm. Schools, universities and businesses closed in many places.

Still, all the preparation may not matter if flooding becomes the greatest threat. In Pascagoula, Miss., Nannette Clark was supervising a work crew installing wood coverings over windows of her more than 130-year-old home. But she said all that won't matter if a storm surge reaches her home, as it did after Katrina in 2005.

"The water was up to the first landing of the stairs," she said. "So I get very nervous about it."

Isaac's approach on the eve of the Katrina anniversary invited obvious comparisons, but Isaac is nowhere near as powerful as the Katrina was when it struck on Aug. 29, 2005. Katrina at one point reached Category 5 status with winds of over 157 mph. It made landfall as a Category 3 storm and created a huge storm surge.

Federal Emergency Management Agency officials said the updated levees around New Orleans are equipped to handle storms stronger than Isaac. Levee failures led to the catastrophic flooding in the area after Katrina.

"It's a much more robust system than what it was when Katrina came ashore," said FEMA Administrator Craig Fugate in a conference call with reporters.

In New Orleans, officials had no plans to order evacuations and instead told residents to hunker down and make do with the supplies they had.

"It's going to be all right," said New Orleans Mayor Mitch Landrieu.

Isaac could pack a watery double punch for the Gulf Coast. If it hits during high tide, Isaac could push floodwaters as deep as 12 feet onto shore in Louisiana, Mississippi and Alabama and up to 6 feet in the Florida Panhandle, while dumping up to 18 inches of rain over the region, the National Weather Service warned.

As of 11 p.m. EDT on Monday, Isaac remained a tropical storm with winds of 70 mph (110 kph). It was centered about 190 miles (305 kms) southeast of the mouth of the Mississippi River, and was moving northwest at 10 mph (17 kph).

The storm's center was forecast to move over the central Gulf of Mexico late Monday and approach the coast of southeastern Louisiana and Mississippi on Tuesday afternoon or Tuesday night, the Hurricane Center said.

On the Alabama coast, Billy Cannon, 72, was preparing to evacuate with several cars packed with family and four Chihuahuas from a home on a peninsula in Gulf Shores. Cannon, who has lived on the coast for 30 years, said he thinks the order to evacuate Monday was premature.

"If it comes in, it's just going to be a big rain storm. I think they overreacted, but I understand where they're coming from. It's safety," he said.

The storm left 24 dead in Haiti and the Dominican Republic, but left little damage in the Florida Keys as it blew past. It promised a soaking but little more for Tampa, where the planned Monday start of the Republican National Convention was pushed back because of the storm.

Only a fraction of an expected 5,000 demonstrators turned out in Tampa to protest GOP economic and social policies outside the convention. Organizers blamed Isaac and a massive police presence for their weak showing.

The storm had lingering effects for much of Florida, including heavy rains and isolated flooding in Miami and points north. Gov. Rick Scott said that as of Monday evening, about 80,000 customers were without power in Florida as a result of the storm.

Scott, a Republican, was returning from the convention in Tampa to Tallahassee to monitor Isaac. Fellow Gulf Coast Republican Govs. Bobby Jindal of Louisiana and Robert Bentley of Alabama said they would not attend the convention at all. Mississippi Gov. Phil Bryant delayed his travel through Wednesday, leaving open the possibility he could attend the final day of the event.

States of emergency were in effect in Louisiana, Mississippi, Alabama and Florida.